High chipping resistance is required for heavy duty tires mounted on large vehicles such as dump trucks, since chipping easily occurs on a tread surface during off-road running, such as running at a mine. Meanwhile, with the heavy duty tire having a plurality of blocks formed on the tread surface thereof, heat easily builds up as a result of the blocks repeatedly deforming when running. Particularly when the tire is used on off-roads, the heat build-up in the blocks tends to cause separation, called heat separation, between a belt layer inside a tread portion and a tread rubber. Thus, high heat resistance is required for the heavy duty tire.
Examples of conventional heavy duty tires having a plurality of blocks formed on the tread surface thereof include a tire disclosed in Japanese Unexamined Patent Application Publication No. H09-136514A. The heavy duty tire disclosed in Japanese Unexamined Patent Application Publication No. H09-136514A is a pneumatic tire having a tread provided with at least one circumferential groove extending in the circumferential direction, a plurality of lateral grooves connected to the circumferential groove and disposed on both sides of a circumferential groove at intervals in the circumferential direction. In this pneumatic tire,
(1) the circumferential groove extends in the circumferential direction within a tread central region that corresponds to 50% of the tread width,
(2) the groove depth of the circumferential groove is 5% or greater of the tread width, and
(3) of the lateral grooves, at least those provided on both sides of the tread have a groove depth that is 109% or greater of that of the circumferential groove.
According to this type of heavy duty tire, both traction performance on bad roads and wet performance at high speed are achieved in a compatible manner.
However, the tire disclosed in Japanese Unexamined Patent Application Publication No. H09-136514A does not have sufficient chipping resistance and heat resistance.